Loud speaker



H. BRM-tsml 1,976,874 LOUD SPEAKER 1 l Filed Dec. 12,* 1932 Patented Oct. 16, 1934 Loco s1 icinnia-VA Henryk Brzeski, Warsaw, Poland 1 Claim. (01.'179-1-155) variations in the exciting current `when this con- The present invention relates to a loud speaker which is improved according to new observations on the nature of the operations involved in the loud speaker in the conversion `of alternating cur- L 5 rents over a considerable .range of frequencies.

. The invention is based on the fact that the sound emitted is considerably' iniiuenced by oscillations or very high frequency and small amplitude, which, however, can be distinguished by the human hearing organs..

Inthe construction' of loud speakers, this fact has hitherto not Vreceived sumcient attention. The loud speakers were so constructed that the magnetic eld produced by the alternating current fiowing throughthe moving coil was considerably effected by the Foucault eddy currents and by hysteresisso that the energy of the oscillations. of high frequency. which influence the quality 'of v.the sound was 'almost entirely lost and 120 the production of a natural tone'by the-loud 130 molecules, as well as Foucault eddy currents which produce considerable losses in energy which is converted into heat. These losses are greater at higher frequencies.

The present invention consists in the use of '35; means whereby the energy losses, due to hysteresis and eddy currents, are diminished. In this way a great improvement in the clearness of the tonesY in reproduction of the human voice or of musical instruments is obtained.

One such means consists in the construction of the loud speaker with two diaphragms provided with coils wound in opposite directions so that the coils produce oppositely directed magnetic elds. The moving coils secured to the diaphragms (cones) are situated at the ends of the magnet which produces a stationary magnetic iield, the diaphragms being situated on a common geometrical axis and being oppositely directed. The magnetic iields produced by the coils are oppositely directed and prevent the lines of magnetic force flowing through the mass oi the stationary magnets or the continuous current electro-magnets.

This arrangement of the two oppositely di- 551 rected moving coils also nullies the effect of sists, for example, of a badly rectied alternating current; The pulsations of such a current act on the two balls in opposite directions so that the resultant eiect is zero.

AV further .meansior diminishing the abovementioned losses consists in making thesurroundings ofthe alternating current coils highly permeable to the magnetic'lines of force. With this object in view, especially the parts otfthe stationary magnets whichv are close to themoving coiliconsists of material 'which is highly permeableto the linesof magnetic force, for example permalloy, ferrocart or of lthin insulated platesgoi such. material. AThese parts of theV stationary magnet may 'also consist of such materials in powdered form pressed together with insulating material, such as bakelite. i

The magnetic current, due tothe moving coils, flows-'for a short distance through` the parts oi the Stationary magnets nearthe coil, the magnetic circuitbeing closed in a line close to the Vcoil windings. 'Ihe'current'loses'none of its strength because no. eddy currents can occur. The element oniwhich themoving coil is wound may also be constructedof a--materal which is highly permeable toithe currents or it can be tted with suchfmaterial at the points `where the magnetic current ows.

In order to avoid the occurrence of resonant oscillations of the moving coils and the cones or diaphragms connected therewith, the cones are ttedwith ends which damp the natural oscillations of the whole system. Some constructional forms of the invention are illustrated diagrammatically in the accompanying drawing.

Fig. 1 is an axial section through a loud speaker with stationary magnets.

Fig. 2 is an axial section through the coil and the magnet in a known construction.

1 UNITED STATES PATENT- oFFica f a Fig. 3 is an axial section through the coils and the magnet in the loud speaker according to the invention.

Fig. 4 shows a part of the section according to Fig. 1 on a larger scale.

Fig. 5 shows the same for another construction.

Figs. 6 and 7 show the connections for the coil windings.

Fig. 2 shows an electro-magnet having a continuous current coil 2 arranged on its iron core 1.

los

The magnetic currents a, produced by the contin- J b excited by the moving coil 4, flows through the whole mass 3 and the iron core 1 of the electromagnet because it remains at the points of smallest magnetic resistance. (The magnetic resistance of the air is a thousand times that of the iron). On account of the variable magnetic current b iiowing through the iron, there are considerable losses due tov hysteresis of 'thel Foucaults eddy currents. This causes l-a distortion ,of the sound waves because in particular the energy of the high frequency oscillations is almost entirely converted into heat and can no longer act on the;

coil 4.

In the diagram shown in Fig. 3 of a loud speaker constructed according to the invention, two moving coils 4 are employed which are arranged symmetrically atboth Aends Vof the iron core 1 of the electro-magnet in such a manner that the windings of the coils 4 aregin opposite directions. The variable magnetic currents b, due to these coils 4, are' oppositely directed and prevent the magnetic lines flowingthrough the whole mass 3 of theelectro-magnet becausethe magnetic currents b flowing in opposite directions through this mass neutralize one another.A On 4account of the difference in magnetic vpotential between the points A and B, themagnetic current takes the form of alineclosely surrounding the Winding of the coils 4. l

In the vicinity of the windings of the moving coils ak path of material of small magnetic resistance is provided for the alternating magnetic current b. This material consists ofthin insulatedpla-tes or of a powder combined withzinsulating material. The magnetic field b is thus not distorted on account of the :production ofeddy currents and the losses due to hysteresis are reduced toaminimum. i y

-In theconstructional form shownn Fig. 1, a stationary magnet 5"is employedf on theends `of which is arranged a disc-likering 6 of iron which is separatedrby the copper ringl'lfromthei iron core 1i. The ring 6 is secured. .to the chassis 8 by means of screws-i9. On the chassis 8,"by means of a ring l0, the diaphragm-in the form of a cone 11 is secured which is provided with an end 12. On the cone 11 is a coil carrier 13 for the moving coil 4 which is arranged between the endsfof 'the iron core 1 and the ring 6. In the iron ring 14 at the end of the iron core 1, small plates-15, for example of permalloy, are embedded. Similar small plates 16 are placed on the inner surface conducting pins 20 which carry the current to the conductor 2l which is insulated from the chassis 8 by means of rings 22 and 23. The ring 22 is connected with the cone ring 25 by radial arms 24, the cone ring 25 being secured to the end 12 of the cone l1 and to the coil carrier 13. The metallic lconductor 21 is laid between the cone ring 25 and the cone 1l with its end 12 to the Windings of the moving coil 4 (Fig. 4).

. The moving coil 4 consists of several layers of Winding which are wound in such a manner that there is a very small potential difference between the separate windings, that is, so that the current flows'fromthe last winding of one layer to the first ofthe next layer. This causes a diminution of the direct flow of current between adjacent windings on account of capacity. The windings of each moving coil 4 can also be divided into two parts 4' and 4", the ends of which are connected by conductors 21 to contacts 18,18 and 18". In such a case, by arranging the coils 4 in parallel (Fig. 6), the potentials of the sections of the winding can be equalized by connecting the contacts 18' through the conductor 1w 26 or' by connecting the contacts 18" with a conductor 27 asshown in Fig. 7, the coils 4 can be arranged in series. The connection of the coils 4 inseries or parallel enables them to be adapted to theamplier.

What I claim is:

A loud speaker comprising a field magnet system, pole pieces on the eld magnets, a speech coil, a former on which the speech coil is wound, suspended between the pole pieces, and having recesses, insertions of material of small magnetic resistance in the recesses cf the former, and insertionsA in the pole pieces of material of small magnetic resistance, for limiting the magnetic field due to the speech currents toa small space around thespeech coil.

HENRYK BRZESKI. 

